Application for such lamp arrays include display boards for advertising and instant replay of information in sports stadiums. One type of such array includes the use of a large number of fluorescent lamps which are arranged in groups of three or more to form pixels. Each pixel contains a light source for each of the primary colors, i.e., blue, red and green. The selective excitation of each pixel in an array of many thousand pixels can provide images similar to television images to observers located at some distance. The relative excitation of the primary color sources within each pixel determines the color which the observer perceives as emanating from that pixel, and, in the aggregate, the color information necessary to perceive entire images in color. Each lamp is coated with a primary color phosphor to emit blue, red or green light.
In the prior art, each lamp contains at least one cathode chosen from the conventional art of fluorescent lamp making. The cathode is suitably impregnated with low work function material, and is a copious source of emitted electrons when raised to some elevated temperature. The lamps also contain a noble gas, e.g., argon, at a low pressure (typically, a few torr) and a small quantity of mercury. Electrons are emitted by the cathode and are accelerated by a voltage applied between the cathode and an anode. Some of the electrons undergo collisions which result in the excitation of mercury atoms, which then emit ultraviolet light at 254 nanometers. This radiation is converted by the phosphor to produce colored light. The anode serves as a collector of the charge flowing in the fluorescent tube and is the electrode which supplies voltage which controls the quantity of electron current, the intensity of the 254 nanometer emission, and therefore, the brightness of the light emitted by the individual pixel element.
Examples of fluorescent lamps or lamp arrays suitable for use in video displays are found in U.S. Pat. Nos. 4,559,480 (Nobs); 4,649,322 (Tellan et al) and 4,665,341 (Imamura et al). Each lamp or lamp array taught in these patents contain at least a pair of electrodes.
One difficulty in using such fluorescent lamps relates to the deleterious effect of the cathode emissive material, which is gradually evaporated at the required elevated temperature and is subsequently deposited on the walls of the phosphor coated lamp. This is one of several mechanisms which gradually diminish the light output of the lamp and is one which is particularly troublesome in lamps of very small dimension. In the large scale display application this gradual dimming is troublesome because of the degradation of image quality, particularly where it may occur on time scales of a few hundred hours. Any imbalance in the aging process can produce uneven image brightness or color and lamp replacements may stand out as exceedingly bright pixels.
Another potential problem area in conventional fluorescent lamp technology is the glass to metal seals employed. While this is a well established technology and can be accomplished with a great deal of reliability, the use of as many as one hundred thousand lamps in a single display places unusually rigid demands on reliability of these seals as well as the electrode structures which they support.
It is clear that there is a need for a display which uses lamps having improved reliability and which are extremely slow to deteriorate.
The individual lamps commonly used are typically operated at power levels near 1 watt. Accordingly, each lamp must be individually supplied with power of this amount totalling as much as 10 to 100 kilowatts for a typical large display. Depending on the requirements of the individual lamps for cathode heating or pre-heating, additional wiring may be required. Power circuitry is costly and complex making construction and repair difficult. A need, therefore, also exists for reduction in the cost and complexity of the wiring and, socketing of the light emitting pixel.